This invention relates to a vehicle body frame of a motor bicycle, and more particularly to a construction of the connecting portion between a head pipe and a frame member.
The vehicle body frame of a motor bicycle has such a role as to support an engine and a power transmission as well as a rider, a load, various equipments, etc., and is the most important vehicle structure for connecting the front and rear wheels. The front portion of the body frame is especially important, since it serves to support an engine and a fuel tank and is connected to a steering head.
The vehicle body frame of a motor bicycle as briefly mentioned above includes a head pipe pivotably supporting a front fork at its front end portion, so that the front fork may be operated freely and a main pipe connected to the head pipe and extending backward of the vehicle body therefrom. And, in a cradle type frame, it further includes a down tube extending downward at an angle. The main pipe and down tube are usually formed of a pipe member such as a steel pipe, etc. The end portions of these pipe members are, either directly or through a gusset, firmly attached to the surface of the head pipe by welding. However, in the conventional construction of the head pipe portion as mentioned above, since two tubular members are required to be welded together, the accuracy of the mating surfaces of the respective members becomes a problem. In order to perform a satisfactory welding, a special attention is especially required.
When the welding is made through the gusset, etc., the number of the component parts becomes large. This means that the number of places where welding is required also increases. In any event, a problem exists in view of productivity.
Particularly, in recent years, there is a tendency that various welding works are automatically made. There are more and more cases where an industiral robot is employed for welding. However, with the above mentioned construction of the welding portions (or places) of the conventional vehicle body frame, even if a welding robot is employed for welding, an easy weld cannot be performed.